flight of fantasy
An imaginative but unrealistic idea. No one took his campaign for office seriously because his proposed solutions to problems were filled with flights of fantasy.
a flight of fancy
or a flight of fantasy
COMMON If you call an idea, statement, or plan a flight of fancy or a flight of fantasy, you mean that it is imaginative but not at all practical. This is no flight of fancy. The prototype is already flying, and production is to begin next year. The idea that you could use these satellites as weapons is a complete flight of fantasy.
a ˌflight of ˈfancy
an idea or a statement that is very imaginative but not practical or sensible: The idea is not just a flight of fancy. It has been done before.